A known inkjet printer includes a print head that has nozzle groups corresponding to respective ink colors. The inkjet printer prints a color image by ejecting ink droplets of respective colors from the corresponding nozzle groups while causing the print head to scan in a main scanning direction. Such a printer may print an image corresponding to a band-shaped unit printing region (e.g., a band region) having the same width as a nozzle width (e.g., a length of a nozzle group) in a single scan by the print head. For implementing image printing onto a printing region having a larger size than a single band region, the printer alternately repeats printing of an image corresponding to a single band region and moving of a print medium in a sub-scanning direction. The inkjet printer may perform bidirectional printing in which printing is performed both when the print head scans in a forward direction of the main scanning direction and when the print head scans in a reverse direction of the main scanning direction. Such bidirectional printing may improve a printing speed as compared with an inkjet printer that performs unidirectional printing in which printing is performed when the print head scans in one of the forward direction and the reverse direction of the main scanning direction only.
Nevertheless, in the bidirectional printing, an ink overlapping order may be different between when the print head scans in the forward direction and when the print head scans in the reverse direction. Such difference in the ink overlapping order may cause a color gap between a result obtained by the forward-direction scanning and a result obtained by the reverse-direction scanning although both printed results represent the same color. Thus, an observer may recognize that the printed results have respective different colors. In order to reduce or prevent occurrence of such a phenomenon, there has been proposed a technique that calculates an index value relating to an estimated ink amount for each block included in a band region and determines, if the index value is greater than a threshold, a specific direction as the scanning direction.